1. Field of the Invention
The present invention relates to a position sensitive photomultiplier, applicable to scintillation imaging technologies in the field of high energy physics and medical applications.
2. Related Background Art
A conventional technique in this technological field, is set forth in "POSITION SENSITIVE PHOTOMULTIPLIER TUBES FOR SCINTILLATION IMAGING" (NSS, 1986). The photomultiplier described has a cross wire anode between a dynode unit constituted by mesh dynodes and a last-stage dynode. Photoelectrons emitted from a photoelectric surface are sequentially cascade-multiplied by the mesh dynode at each stage, thereby emitting secondary electrons. The secondary electrons pass through the cross wire anode and are further multiplied by the last-stage dynode.
The secondary electrons multiplied by the last-stage dynode and orbit-inverted are captured by the cross wire anode and extracted from the photomultiplier.
The cross wire anode consists of two layers of anode groups in the X and Y directions perpendicular to each other. Each anode group is constituted by a plurality of wires arranged at a pitch of 3.0 to 7.0 mm and having a diameter of 0.5 to 1.0 mm. These wires are connected by resistor chains constituted by resistors connected in series. Secondary electrons extracted from wires of the upper and lower wire anode are shunted through the resistor chains and extracted from terminals X.sub.1 and X.sub.2 of one of the resistor chains and terminals Y.sub.1 and Y.sub.2 of another of the resistor chains. The terminals X.sub.1 and X.sub.2 are terminals of an X-component shunt circuit (resistor chain) constituted by resistors for electrically connecting between the wires of the upper wire anode. The terminals Y.sub.1 and Y.sub.2 are terminals of a Y-component shunt circuit (resistor chain) constituted by resistors for electrically connecting between the wires of the lower wire anode. By connecting an adder and a divider to each terminal, the position of the center of gravity in the X and Y directions can be obtained on the basis of the following equations: EQU X=X.sub.2 /(X.sub.1 +X.sub.2) EQU Y=Y.sub.2 /(Y.sub.1 +Y.sub.2)
The position (X, Y) means an incident position of a plane of incidence, where an incident weak light beam is reached.